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    <font size="7">Filesystem Library<br/>
    Version 4</font>
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    <td><a href="index.htm">Home</a> &nbsp;&nbsp;
    <a href="tutorial.html">Tutorial</a> &nbsp;&nbsp;
    <a href="reference.html">Reference</a> &nbsp;&nbsp;
    <a href="faq.htm">FAQ</a> &nbsp;&nbsp;
    <a href="release_history.html">Releases</a> &nbsp;&nbsp;
    <a href="portability_guide.htm">Portability</a> &nbsp;&nbsp;
    <a href="v4.html">V4</a> &nbsp;&nbsp;
    <a href="v3.html">V3 Intro</a> &nbsp;&nbsp;
    <a href="v3_design.html">V3 Design</a> &nbsp;&nbsp;
    <a href="deprecated.html">Deprecated</a> &nbsp;&nbsp;
    <a href="issue_reporting.html">Bug Reports</a>&nbsp;&nbsp;
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      <i><b>Contents</b></i></td>
  </tr>
  <tr>
    <td width="100%" bgcolor="#E8F5FF">
    <a href="#Introduction">Introduction</a><br/>
    <a href="#Documentation">Documentation</a><br/>
    <a href="#Using">Using the library</a><br/>
    <a href="#Coding-guidelines">Coding guidelines</a><br/>
    <a href="#Cautions">Cautions</a><br/>
    <a href="#Headers">Headers</a><br/>
    <a href="#Examples">Example programs</a><br/>
    <a href="#Implementation">Implementation</a><br/>
    <a href="#Macros">Macros</a><br/>
    <a href="#Building">Building the object-library</a><br/>
    <a href="#Cygwin">Notes for Cygwin users</a><br/>
    <a href="#Change-history">Version history<br/>
&nbsp; with acknowledgements</a></td>
  </tr>
  </table>
<p></p>
<h2><a name="Introduction">Introduction</a></h2>
<p>The Boost.Filesystem library provides facilities to manipulate files and directories,
and the paths that identify them.</p>

<p>The features of the library include:</p>

<ul>
  <li><b>A modern C++ interface, highly compatible with the C++ standard
  library.</b></li>
</ul>
<blockquote>
  <blockquote>

<p>Many users say the interface is their primary motivation for using
Boost.Filesystem. They like its use of familiar idioms based on standard library
containers, iterators, and algorithms. They like having errors reported by
throwing exceptions.</p>

  </blockquote>
</blockquote>
<ul>
  <li><b>Portability between operating systems.</b><br/>
&nbsp;<ul>
    <li>At the C++ syntax level, it is convenient to learn and use one interface
    regardless of the operating system.</li>
    <li>At the semantic level, behavior of code is reasonably portable across
    operating systems.</li>
    <li>Dual generic or native path format support encourages program
    portability, yet still allows communication with users in system specific
    formats.<br/>
&nbsp;</li>
  </ul>
  </li>
  <li><b>Error handling and reporting via C++ exceptions (the default) or error
  codes.</b><br/>
&nbsp;<ul>
    <li>C++ exceptions are the preferred error reporting mechanism for most
    applications. The exception thrown includes the detailed error code
    information important for diagnosing the exact cause of file system errors.</li>
    <li>Error reporting via error code allows user code that provides detailed
    error recovery to avoid becoming so littered with try-catch blocks as to be
    unmaintainable. <br/>
&nbsp;</li>
  </ul>
  </li>
  <li><b>Suitable for a broad spectrum of applications, ranging from simple
  script-like operations to extremely complex production code.</b><br/>
&nbsp;<ul>
    <li>At the simple script-like end of the spectrum, the intent is not to
    compete with Python, Perl, or shell languages, but rather to provide
    filesystem operations when C++ is already the language of choice.</li>
    <li dir="ltr">
    <p dir="ltr">Finer grained control over operations and error handling is available to
    support more complex applications or other cases where throwing exceptions
    isn't desired.<br/>
&nbsp;</p></li>
  </ul>
  </li>
  <li>
  <p dir="ltr"><b>Forms the basis for
  <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n4100.pdf">
  ISO/IEC TS 18822</a>, the C++ standard library Filesystem Technical
  Specification.</b></p></li>
</ul>

<h2><a name="Documentation">Documentation</a></h2>

<p><b><a href="tutorial.html">Tutorial</a></b> - A gentle introduction to
the library, with example programs provided for you to experiment with.</p>

<p><b><a href="reference.html">Reference</a></b> - Formal documentation in the
style of the C++ standard for
every component of the library.</p>

<p><b><a href="faq.htm">FAQ</a></b> - Frequently asked questions.</p>

<p><b><a href="portability_guide.htm">Portability Guide</a></b> - Help for those
concerned with writing code to run on multiple operating systems.</p>

<p><b><a href="deprecated.html">Deprecated Features</a></b> - Identifies
deprecated features and their replacements.</p>

<p><b><a href="v4.html">Version 4 Description</a></b> - Summary of changes from
Version 3.</p>

<p><b><a href="v3.html">Version 3 Introduction</a></b> - Aimed at users of prior
Boost.Filesystem versions.</p>

<p><b><a href="v3_design.html">Version 3 Design</a></b> - Historical document
from the start of the Version 3 design process.</p>

<p><b><a href="design.htm">Original Design</a></b> - Historical document from
the start of the Version 1 design process.</p>

<p><b><a href="do_list.html">Do List</a></b> - Boost.Filesystem development work
in the pipeline.</p>

<h2><a name="Using">Using</a> the library</h2>
<p>Boost.Filesystem is implemented as a separately compiled library, so  you must install
binaries in a location that can be found by your linker. If you followed the
<a href="http://www.boost.org/doc/libs/release/more/getting_started/index.html">Boost Getting Started</a> instructions, that's already been done for you.</p>
<h2><a name="Coding-guidelines">Coding guidelines</a></h2>
<p>For new code, defining <code>BOOST_FILESYSTEM_NO_DEPRECATED</code> before
including filesystem headers is strongly recommended. This prevents inadvertent
use of old features, particularly legacy function names, that have been replaced
and are going to go away in the future.</p>
<h2><a name="Cautions">Cautions</a></h2>
<p>After reading the tutorial you can dive right into  simple,
script-like programs using the Filesystem Library! Before doing any serious
work, however, there a few cautions to be aware of:</p>
<h4><b>Effects and Postconditions not guaranteed in the presence of race-conditions</b></h4>
<p>Filesystem function specifications follow the C++ Standard Library form, specifying behavior in terms of
effects and postconditions. If
a <a href="reference.html#Race-condition">race-condition</a> exists, a function's
postconditions may no longer be true by the time the function returns to the
caller.</p>
<blockquote>
<p><b><i>Explanation: </i></b>The state of files and directories is often
globally shared, and thus may be changed unexpectedly by other threads,
processes, or even other computers having network access to the filesystem. As an
example of the difficulties this can cause, note that the following asserts
may fail:</p>
<blockquote>
<p><code>assert( exists( &quot;foo&quot; ) == exists( &quot;foo&quot; ) );&nbsp; //
(1)<br/>
<br/>
remove_all( &quot;foo&quot; );<br/>
assert( !exists( &quot;foo&quot; ) );&nbsp; // (2)<br/>
<br/>
assert( is_directory( &quot;foo&quot; ) == is_directory( &quot;foo&quot; ) ); //
(3)</code></p>
</blockquote>
<p>(1) will fail if a non-existent &quot;foo&quot; comes into existence, or an
existent &quot;foo&quot; is removed, between the first and second call to <i>exists()</i>.
This could happen if, during the execution of the example code, another thread,
process, or computer is also performing operations in the same directory.</p>
<p>(2) will fail if between the call to <i>remove_all()</i> and the call to
<i>exists()</i> a new file or directory named &quot;foo&quot; is created by another
thread, process, or computer.</p>
<p>(3) will fail if another thread, process, or computer removes an
existing file &quot;foo&quot; and then creates a directory named &quot;foo&quot;, between the
example code's two calls to <i>is_directory()</i>.</p>
</blockquote>
<h4><b>Exceptions</b></h4>
<p>Unless otherwise specified, Boost.Filesystem functions throw <i>
<a href="reference.html#basic_filesystem_error-constructors">basic_filesystem_error</a></i>
exceptions to report failures such as I/O errors. Implementations may also use C++ Standard Library functions
which can throw <i>std::bad_alloc </i>exceptions to report memory allocation
errors. These exceptions may be thrown even
though the error condition leading to the exception is not explicitly specified
in the function's &quot;Throws&quot; paragraph.</p>
<p>Nominally non-throwing versions are provided for
<a href="reference.html#Operational-functions">operational functions</a> that
access the external file system, since these are often used
in contexts where error codes may be the preferred way to report an error. Even
the nominally non-throwing versions of functions will throw <i>std::bad_alloc </i>
exceptions to report memory allocation errors. However, functions marked <code>
noexcept</code> never throw exceptions.</p>

<h2><a name="Headers">Headers</a></h2>

<p>The Boost.Filesystem library provides several&nbsp;headers:</p>

<ul>
  <li>Header &lt;<a href="../../../boost/filesystem.hpp">boost/filesystem.hpp</a>&gt;
  provides access to all features of the library, except file streams.<br/>
&nbsp;</li>
  <li>Header &lt;<a href="../../../boost/filesystem/fstream.hpp">boost/filesystem/fstream.hpp</a>&gt;
  inherits the same components as the C++ Standard
  Library's <i>fstream</i> header, but files are identified by <code>const path&amp;</code>
  arguments rather that <code>const char*</code> arguments.</li>
</ul>

<h2><a name="Examples">Example programs</a></h2>
<p>See the <a href="tutorial.html">tutorial</a> for example programs.</p>
<h2><a name="Implementation">Implementation</a></h2>
<p>The current implementation supports operating systems which provide
the POSIX or Windows API's.</p>
<p>The library is in regular use on Apple  OS X, HP-UX, IBM AIX, Linux,
Microsoft Windows, SGI IRIX, and Sun Solaris operating systems using a variety
of compilers. It is also used by several smart phone operating systems.</p>

<h2><a name="Macros">Macros</a></h2>
<p>Users may define the following macros if desired. Sensible defaults are
provided, so users can ignore these macros unless they have special needs.</p>
<table border="1" cellpadding="5" cellspacing="0" style="border-collapse: collapse" bordercolor="#111111">
  <tr>
    <td><b><i>Macro Name</i></b></td>
    <td><b><i>Default</i></b></td>
    <td><b><i>Effect if defined</i></b></td>
  </tr>
  <tr>
    <td valign="top"><code>BOOST_FILESYSTEM_VERSION</code></td>
    <td valign="top">3</td>
    <td valign="top">Selects the Boost.Filesystem library version. Can have values of 3 or 4.
      Defining to 4 also implies <code>BOOST_FILESYSTEM_NO_DEPRECATED</code>.</td>
  </tr>
  <tr>
    <td valign="top"><code>BOOST_FILESYSTEM_NO_DEPRECATED</code></td>
    <td valign="top">Not defined.</td>
    <td valign="top">Deprecated features are excluded from headers.</td>
  </tr>
  <tr>
    <td valign="top"><code>BOOST_FILESYSTEM_DYN_LINK</code></td>
    <td valign="top">Defined if <code>BOOST_ALL_DYN_LINK</code> is defined,
    otherwise not defined.</td>
    <td valign="top">The Boost.Filesystem library is dynamically linked. If not defined,
    static linking is assumed.</td>
  </tr>
  <tr>
    <td valign="top"><code>BOOST_FILESYSTEM_NO_LIB</code></td>
    <td valign="top">Defined if <code>BOOST_ALL_NO_LIB</code> is defined,
    otherwise not defined.</td>
    <td valign="top">Boost.Filesystem library does not use the Boost auto-link
    facility.</td>
  </tr>
  <tr>
    <td valign="top"><code>BOOST_FILESYSTEM_DISABLE_SENDFILE</code></td>
    <td valign="top">Not defined. <code>sendfile</code> API presence detected at library build time.</td>
    <td valign="top">Boost.Filesystem library does not use the <code>sendfile</code> system call on Linux. The <code>sendfile</code> system call started accepting regular file descriptors as the target in Linux 2.6.33.</td>
  </tr>
  <tr>
    <td valign="top"><code>BOOST_FILESYSTEM_DISABLE_COPY_FILE_RANGE</code></td>
    <td valign="top">Not defined. <code>copy_file_range</code> API presence detected at library build time.</td>
    <td valign="top">Boost.Filesystem library does not use the <code>copy_file_range</code> system call on Linux. The <code>copy_file_range</code> system call was introduced in Linux kernel 4.5 and started operating across filesystems in 5.3.</td>
  </tr>
  <tr>
    <td valign="top"><code>BOOST_FILESYSTEM_DISABLE_STATX</code></td>
    <td valign="top">Not defined. <code>statx</code> presence detected at library build time.</td>
    <td valign="top">Boost.Filesystem library does not use the <code>statx</code> system call on Linux. The <code>statx</code> system call was introduced in Linux kernel 4.11.</td>
  </tr>
  <tr>
    <td valign="top"><code>BOOST_FILESYSTEM_DISABLE_GETRANDOM</code></td>
    <td valign="top">Not defined. <code>getrandom</code> API presence detected at library build time.</td>
    <td valign="top">Boost.Filesystem library does not use the <code>getrandom</code> system call on Linux. The <code>getrandom</code> system call was introduced in Linux kernel 3.17.</td>
  </tr>
  <tr>
    <td valign="top"><code>BOOST_FILESYSTEM_DISABLE_ARC4RANDOM</code></td>
    <td valign="top">Not defined. <code>arc4random</code> API presence detected at library build time.</td>
    <td valign="top">Boost.Filesystem library does not use the <code>arc4random_buf</code> system call on BSD systems. The <code>arc4random</code> API was introduced in OpenBSD 2.1 and FreeBSD 8.0.</td>
  </tr>
  <tr>
    <td valign="top"><code>BOOST_FILESYSTEM_DISABLE_BCRYPT</code></td>
    <td valign="top">Not defined. BCrypt API presence detected at library build time.</td>
    <td valign="top">Boost.Filesystem library does not use the BCrypt API on Windows. Has no effect on other platforms.</td>
  </tr>
</table>
<p>User-defined BOOST_POSIX_API and BOOST_WINDOWS_API macros are no longer
supported.</p>
<h2><a name="Building">Building</a> the object-library</h2>
<p>The object-library will  be built automatically if you are using the Boost
build system. See
<a href="../../../more/getting_started.html">Getting Started</a>. It can also be
built manually using a <a href="../build/Jamfile.v2">Jamfile</a>
supplied in directory libs/filesystem/build, or the user can construct an IDE
project or make file which includes the object-library source files.</p>
<p>The object-library source files are
supplied in the <a href="../src">src directory</a>. These source files implement the
library for POSIX or Windows compatible operating systems; no implementation is
supplied for other operating systems. Note that many operating systems not
normally thought of as POSIX  systems, such as mainframe legacy
operating systems or embedded operating systems, support POSIX compatible file
systems and so will work with the Filesystem Library.</p>
<p>The object-library can be built for static or dynamic (shared/dll) linking.
This is controlled by the BOOST_ALL_DYN_LINK or BOOST_FILESYSTEM_DYN_LINK
macros. See the <a href="http://www.boost.org/development/separate_compilation.html">Separate
Compilation</a> page for a description of the techniques used.</p>
<h3>Note for <a name="Cygwin">Cygwin</a> users</h3>
<p> <a href="http://www.cygwin.com/">Cygwin</a> version 1.7 or later is
required because only versions of GCC with wide character strings are supported.</p>

<p> The library's implementation code treats Cygwin as a Windows platform, and
thus uses the Windows API and uses Windows path syntax as the native path
syntax.</p>

<h2><a name="Change-history">Version history</a></h2>

<h3>Version 4</h3>

<p><b>Under development</b> - Improve compatibility with std::filesystem introduced in C++17
(original proposal: <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n4099.html">ISO
C++ File System Technical Specification</a>). The Filesystem TS was based on
Boost.Filesystem Version 3, with only a small number of changes. Most user code
written for Version 3 should work unchanged with Version 4. The differences can be seen in a
<a href="v4.html">separate section</a>.</p>

<h3>Version 3</h3>

<p>Boost 1.44.0 - June, 2010 - Internationalization via single class <code>path</code>.
More uniform error handling.</p>

<p>Peter Dimov suggested use of a single path class rather than a <code>basic_path</code>
class template. That idea was the basis for the Version 3 redesign.</p>

<p>Thanks for comments from Robert Stewart, Zach Laine, Peter Dimov, Gregory
Peele, Scott McMurray, John Bytheway, Jeff Flinn, Jeffery Bosboom.</p>

<h3>Version 2</h3>

<p>Boost 1.34.0 - May, 2007 - Internationalization via <code>basic_path</code>
template.</p>

<p>So many people have contributed comments and bug reports that it isn't any
longer possible to acknowledge them individually. That said, Peter Dimov and Rob
Stewart need to be specially thanked for their many constructive criticisms and
suggestions. Terence
Wilson and Chris Frey contributed timing programs which helped illuminate
performance issues.</p>

<h3>Version 1</h3>

<p>Boost 1.30.0 - March, 2003 - Initial official Boost release.</p>

<p>The Filesystem Library was designed and implemented by Beman Dawes. The
original <i>directory_iterator</i> and <i>filesystem_error</i> classes were
based on prior work from Dietmar Kühl, as modified by Jan Langer. Thomas Witt
was a particular help in later stages of initial development. Peter Dimov and
Rob Stewart made many useful suggestions and comments over a long period of
time. Howard Hinnant helped with internationalization issues.</p>

<p>Key <a href="design.htm#Requirements">design requirements</a> and
<a href="design.htm#Realities">design realities</a> were developed during
extensive discussions on the Boost mailing list, followed by comments on the
initial implementation. Numerous helpful comments were then received during the
Formal Review. Participants included
Aaron Brashears,
Alan Bellingham,
Aleksey Gurtovoy,
Alex Rosenberg,
Alisdair Meredith,
Andy Glew,
Anthony Williams,
Baptiste Lepilleur,
Beman Dawes,
Bill Kempf,
Bill Seymour,
Carl Daniel,
Chris Little,
Chuck Allison,
Craig Henderson,
Dan Nuffer,
Dan'l Miller,
Daniel Frey,
Darin Adler,
David Abrahams,
David Held,
Davlet Panech,
Dietmar Kühl,
Douglas Gregor,
Dylan Nicholson,
Ed Brey,
Eric Jensen,
Eric Woodruff,
Fedder Skovgaard,
Gary Powell,
Gennaro Prota,
Geoff Leyland,
George Heintzelman,
Giovanni Bajo,
Glen Knowles,
Hillel Sims,
Howard Hinnant,
Jaap Suter,
James Dennett,
Jan Langer,
Jani Kajala,
Jason Stewart,
Jeff Garland,
Jens Maurer,
Jesse Jones,
Jim Hyslop,
Joel de Guzman,
Joel Young,
John Levon,
John Maddock,
John Williston,
Jonathan Caves,
Jonathan Biggar,
Jurko,
Justus Schwartz,
Keith Burton,
Ken Hagen,
Kostya Altukhov,
Mark Rodgers,
Martin Schuerch,
Matt Austern,
Matthias Troyer,
Mattias Flodin,
Michiel Salters,
Mickael Pointier,
Misha Bergal,
Neal Becker,
Noel Yap,
Parksie,
Patrick Hartling, Pavel Vozenilek,
Pete Becker,
Peter Dimov,
Rainer Deyke,
Rene Rivera,
Rob Lievaart,
Rob Stewart,
Ron Garcia,
Ross Smith,
Sashan,
Steve Robbins,
Thomas Witt,
Tom Harris,
Toon Knapen,
Victor Wagner,
Vincent Finn,
Vladimir Prus, and
Yitzhak Sapir.
</p>

<p>A lengthy discussion on the C++ committee's library reflector illuminated the &quot;illusion
of portability&quot; problem, particularly in postings by PJ Plauger and Pete Becker.</p>

<p>Walter Landry provided much help illuminating symbolic link use cases for
version 1.31.0.&nbsp;</p>

<hr/>

<p>&copy; Copyright Beman Dawes, 2002-2005</p>
<p>&copy; Copyright Andrey Semashev, 2021</p>
<p> Use, modification, and distribution are subject to the Boost Software
License, Version 1.0. See <a href="http://www.boost.org/LICENSE_1_0.txt">
www.boost.org/LICENSE_1_0.txt</a></p>

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